1. Field of the Invention
The invention relates in general to a wireless communication system, and more particularly, to a technique for detecting data packets.
2. Description of the Related Art
A wireless local area network (WLAN) system transceives data in a unit of packets. To lower possibilities of collisions between packets so as to enhance transmission quality, two successive packets are transmitted with a constant time interval in between. Such time interval is usually 16 μs, and is referred to as a short interframe space (SIFS) interval.
FIG. 1(A) shows a schematic diagram of a relationship between packets with the SIFS interval. A decoding latency is in general present at a receiver. Taking FIG. 1(A) for example, a time point t12 at which the receiver finishes decoding a first packet 11 is later than a time point t11 at which the first packet 11 is completely transmitted to the receiver. The interval between the time points t11 and t12 is the decoding latency. After finishing decoding the first packet 11, the receiver starts detecting whether a next packet exists in the transmission channel. A preamble at the beginning of a packet is a reference for the receiver to determine the existence of a packet, and is predetermined data having a total length of 8 μs. In the example in FIG. 1(A), after identifying the preamble (the shaded area) of the second packet 12, at a time point t13, the receiver confirms the existence of the second packet 12 and then starts decoding the second packet 12.
In the 802.11n specifications, a packet format having a shorter interval is defined for promoting network transmission efficiency. The length of such reduced interframe space (RIFS) is only 2 μm. FIG. 1(B) shows a schematic diagram of a relationship between packets with the RIFS interval. The receiver finishes decoding a third packet 13 at a time point t14. As seen from FIG. 1(B), due to the decoding latency, the time point t14 at which the receiver starts detecting the existence of a next packet is later than a time point t15 at which the transmission of the preamble of a fourth packet 14 ends. Not until a time point t16, the receiver cannot identify the preamble of a fifth packet 15 and start decoding the fifth packet 15. It is apparent that the receiver misses data carried in the fourth packet 14. One solution for solving the above issue is to utilize a circuit with a faster computation speed at the receiver to shorten the decoding latency, and to thus bring forward the time point t14 to be earlier than the time point t15. However, such solution not only significantly increases hardware costs but also poses addition power consumption on the receiver.